Increase in Histone Methylation in the Cat Germinal Vesicle Related to Acquisition of Meiotic and Developmental Competence.

Contents This study identified specific changes in histone lysine methylation patterns of the feline germinal vesicle ( GV) during pre-antral-to-antral follicle transition, the latter being a key interval for competence acquisition. Oocytes from adult cats were isolated from pre-antral, early (≤0.5 mm diameter), small (0.6-1 mm) or large (1-3.5 mm) antral follicles and immuno-stained with anti-histones H3 trimethylated at lysine 9 ( H3 K9me3), lysine 4 ( H3 K4me3), lysine 27 ( H3 K27me3) or H3 dimethylated at lysine 79 ( H3 K79me2). The vast majority of oocytes (range, 72.2-85.4%; p > 0.05) contained a GV with H3 K9me3 or H3 K27me3, regardless of follicular stage/size. However, the proportion of GVs with H3 K4me3 or H3 K79me2 was higher in early antral follicles (42.6%; p < 0.05) compared with other stages (range, 12.1-15.2%). Therefore, H3 K4me3 and H3 K79me2 (both known to be associated with selective gene activation) appear to be reliable markers of onset of GV competence during the pre-antral-to-antral transition phase. By contrast, H3 K9me3 and H3 K27me3 (both known to be related to selective gene repression) seem more linked to expression patterns during the GV stage and are less useful indicators during the entire folliculogenesis interval. [ABSTRACT FROM AUTHOR]